The myproxy-logon program in MyProxy versions 5.0 through 5.2 does not
enforce the check that the myproxy-server's certificate contains the
expected hostname or identity. The impacted MyProxy versions are
included in Globus Toolkit releases 5.0.0-5.0.2. This issue is
addressed in MyProxy 5.3.

Full details are available:
http://grid.ncsa.illinois.edu/myproxy/security/myproxy-adv-2011-01.txt

Other changes in this release:

if myproxy-logon GSI mutual authentication with the myproxy-server fails, try again with client-side anonymous authentication, in case the client-side GSI credentials are unacceptable to the myproxy-server (for example, signed by an untrusted CA), but the myproxy-server would accept an anonymous client (http://bugzilla.globus.org/bugzilla/show_bug.cgi?id=7103)